How to Exterminate Moss on a Roof

Addressing the shady, humid conditions that favor moss development offers the most effective long-term control.

Although moss, lichens or algae growing on a roof or other structure do not directly harm the roof, they are sometimes considered unsightly and can trap moisture against the roofing. Moss and algae are generally most problematic in areas that have high rainfall and humidity. North-facing or shaded roof surfaces also favor moss growth. Moss is fairly easy to remove and prevent on a roof, though any work done on the roof can present challenges.

1

Trim off or selectively thin out branches that hang over the mossy area of the roof using a pole saw or other appropriate pruning tools. This method alone may decrease the shade and increase light penetration enough to effectively dry out the moss and prevent future occurrences.

2

Brush moss off the roof with a stiff-bristled brush. Use only downward strokes and only use a brush that does not damage the roofing material. To completely remove the moss, you may need to use a single bristle or wire to force out moss from between individual shingles.

3

Spray a strong stream of water down the roof to knock moss off. Only use a power washer if it will not harm or cut into the roofing materials and always direct the stream of water downward.

4

Apply a moss killer to the roof according to the manufacturer's directions. Multiple products are available that kill moss and offer varying degrees of effectiveness and levels of potential harm to vegetation and nearby aquatic life. Potassium salts of fatty acids are noncorrosive, nonstaining and biodegradable, with low negative environmental impact, although they should not come into contact with water sources.

5

Nail a strip of zinc or galvanized flashing to the ridge cap along the roof peak on each side of the roof where moss is present. Pound a nail every foot along the length of the strip to secure it. With each rain event, zinc leaches off the strip and kills or retards the growth of moss in an area up to 15 feet below the strip. For larger roofs, an additional strip or copper wire situated 15 feet below the ridge or midway down the roof is warranted. The zinc strip can control moss for decades and is most effective if you remove existing moss prior to strip installation.

6

Brush leaves, branches and other debris off of the roof regularly to decrease moisture retention and permit more light to reach the roof.

Things You Will Need

Pole saw, loppers and other pruning tools

Stiff-bristled brush

Wire, if needed

Power washer

Chemical moss killer

Zinc strip

Nails

Hammer

Tips

Products to kill moss work most effectively when applied during a spell of dry weather within a wet season when moss is actively growing.

Warnings

Use caution and follow safe operating guidelines when trimming overhanging branches with a pole saw or any other tool.

Be careful when working on a roof, especially if the roof is wet or moss is present. Do not attempt to work on a roof with a steep slope.